As we have seen in Chapter 1, in a transmission line system which has a reference characteristic impedance of Z o any termination or line which has an impedance other than Z o will cause reflections of power to be set up. Any devices such as diodes, transistors, mixers and antennas are almost certain to have an impedance different from Z o . With devices, circuits or subsystems having different impedances connected into a system, a series of reflections will be set up within the overall system which will certainly degrade the overall performance of the system and may well damage sensitive components if large power levels are reflected. Assessing the risk of this occurring and/or predicting the reduction in performance is a very complex task. In general it is much better to try and ensure that all circuits and subsystems have port impedances equal to some system characteristic impedance. If this is the case then the system can be assembled without worrying about internal reflections.
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